The present invention relates to packet-switching communications networks, and more particularly, to the integration of Signaling System Number 7 (SS7) networks with more recently developed data communications (datacom) networks utilizing Multi-Protocol Label Switching (MPLS).
Today, communications networks are designed using layered architectures in which peer processes residing on different nodes within a network communicate without regard to the detailed operation of the lower-layer processes required to carry out that communication. Advantageously, such layered architectures result in standard, interchangeable and widely available network modules.
Most of the layered networks of today resemble the seven-layer Open Systems Interconnection (OSI) reference model put forth by the International Standards Organization (ISO). See, for example, D. Bertsekas and R. Gallager, Data Networks, Prentice-Hall, Inc., 1987, pp. 14-26. According to the OSI reference, a network includes, from lowest to highest level of abstraction, a physical layer, a data link layer, a network layer, a transport layer, a session layer, a presentation layer, and an application layer.
The physical layer (or layer 1) provides a virtual link for transmitting sequences of bits between any pair of nodes in a network, while the data link layer (or layer 2) performs error-checking and other functions to convert the potentially unreliable bit pipes of layer 1 into reliable links for bi-directional transmission of data packets (i.e., groups or frames of bits) between nodes. Additionally, the network layer (or layer 3) provides routing and flow control for data packets passing through and within the network, while the transport, session, presentation and application layers (layers 4-7, respectively) provide increasingly higher levels of functionality which are well known in the art of network design.
Most datacom networks of today (e.g., the networks used to implement the well known Internet) generally adhere to the above described layered architecture. More specifically, datacom networks typically utilize any of a number of widely available network layer protocols for packet routing and flow control, as well as any of a number of available data link layer protocols for error-checking, etc. Thus, as shown in FIG. 1, an exemplary datacom network 100 can incorporate a number of network protocols 110, including the well known Apple Talk(trademark) protocol and various versions of the equally well known Internet Protocol (IPv6, IPv4, IPX). As is also shown in the figure, the exemplary network 100 can further incorporate a number of data link protocols 120, including the Ethernet (ET) protocol, the Fiber Distribution Data Interface (FDDI) protocol, the Asynchronous Transfer Mode (ATM) protocol, the Frame Relay (FR) protocol, and the Point-to-Point protocol (PPP), each of which is well known in the art.
Conventionally, routing of packets in an IP-based network is performed entirely at the network layer. Specifically, upon a data packet arriving at a network node, or router, the network-layer process operating at the node compares a destination address included with the packet to a list of address prefixes stored within a routing table maintained at the node. Upon finding a longest matching prefix, the node then forwards the packet on to another node associated with the longest matching prefix (i.e., to a xe2x80x9cnext hopxe2x80x9d router), where the matching process is repeated. In this way, packets hop from node to node, ultimately making it to the packet destination address (and ideally via a best path).
Recently, MPLS technology has been developed to reduce the amount of time and computational resources used in the above described routing mechanism. More specifically, MPLS replaces the need to do the longest prefix match at each router by inserting a fixed length label between the network layer header and the link layer header of each data packet. As is described in more detail hereinafter, a router can thus easily make a next hop decision for an incoming packet merely by using the MPLS label of the packet as an index into a routing table. As shown in FIG. 2, label switching provides an abstraction layer 210 between the network layer protocols 110 and the link layer protocols 120.
Like the above described IP-based networks, the well known SS7 standard (which is used, for example, in implementing many of today""s wireless communications systems) is modeled after the OSI seven-layer reference model. See, for example, T. Rappaport, Wireless Communications Principles and Practice, Prentice Hall, Inc., 1996, pp. 463-472.
Thus, as shown in FIG. 3, an exemplary SS7 system 300 includes, among other parts, a first Message Transfer Part (MTP) 310, a second MTP 320, a third MTP 330, a Signaling Connection Control Part (SCCP) 340, and an Integrated Services Digital Network User Part (ISDN User Part, or ISUP) 350. As shown, the first MTP 310 is analogous to the OSI physical layer (layer 1), the second MTP 320 is analogous to the OSI data link layer (layer 2), and the third MTP 330 is analogous to the OSI network layer (layer 3). Additionally, the SCCP 340 and the ISUP 350 perform certain layer 3 and higher functions.
Although both the SS7 standard and the above described IP-based networks are all modeled on the OSI seven-layer reference, the SS7 and IP-based routing mechanisms are sufficiently different that the above described MPLS scheme (developed specifically for IP-based networks) cannot be directly applied in the context of an SS7 network. Consequently, recent efforts to integrate legacy SS7-based telephony systems with next generation systems based on IP-type packet switching technologies (e.g., IP, ATM, etc.), have been difficult.
Although many vendors have already proposed solutions on how SS7 networks can interwork with the IP domain, such solutions have proven unsatisfactory in many respects. Known solutions either use some form of IP encapsulation of SS7 messages, or some form of mapping of SS7 messages into IP Session Initiation Protocol (SIP) messages or H.323 messages, etc. As a result, the known solutions are generally inefficient and do not guarantee a high degree of performance. Consequently, there is a need for improved methods and apparatus for integrating SS7 networks with MPLS-based datacom networks.
The present invention fulfills the above-described and other needs by providing techniques for implementing MPLS directly in the SS7 protocol stack. As a result, SS7 MTP3 and MTP3bare now additional network layers that can interface, via MPLS, with literally any link layer technology. Consequently, label switching technology can be used seamlessly throughout a collection of heterogeneous networks, including both IP-based and SS7-based networks. Advantageously, the present invention does not merely map messages between IP and SS7 formats, but instead addresses the problem at large by truly integrating the SS7 and IP-based domains.
According to the invention, an exemplary method of routing Signaling System Number 7 (SS7) data packets through a heterogeneous packet-switching network using Multi-Protocol Label Switching (MPLS) includes the steps of: establishing an MPLS forwarding equivalence class (FEC), at least one element of the FEC being an SS7 destination; associating a label with the FEC at a first router in the heterogeneous packet switching network; attaching the label, at the first router, to a data packet belonging to the FEC; and forwarding the labeled data packet from the first router to a second router in the communications network. The SS7 destination can be, for example, a Destination Point Code (DPC), a Signaling Connection Control Part (SCCP) global title, or an SCCP subsystem number (SSN).
The exemplary method can further include the step of advertising (e.g., via a label distribution protocol, or LDP) the label associated with the FEC at the first router to other routers in the communications network. Additionally, the first router can maintain a label information table including a plurality of FECs and associated labels (a number of the FECs including SS7-based elements and another number of FECs including non-SS7-based elements), and can thus serve as a destination for both SS7 data packets and non-SS7 data packets.
An exemplary MPLS router according to the invention includes: a routing table for storing information relating to an MPLS FEC, wherein an element of the FEC can be a Signaling System Number 7 (SS7) destination; and a label switching protocol processor for associating a label with the FEC, attaching the label to a data packet belonging to the FEC, and forwarding the labeled data packet to another router in the communications network. The exemplary router can further include a label distribution processor configured to advertise the label associated with the FEC to other routers in the communications network.